This invention relates to manually releasable parking brake devices as are used on transit vehicles, such parking brakes which can be of a spring-applied, air-released type. A situation may exist where the parking brake will not release due to low or no air pressure available; therefore, the quick-release apparatus must be manually operable. It is common for such parking brake to be separate from the individual tread brake units, and that the tie-in-point be a brake lever on which the tread brake and parking brake both connect. As such, one of the requirements is that such parking brake devices occupy as little mounting space as possible which, in turn, results in a small space to mount and operate the manual release portion. Typically, parking brake manual-release mechanisms have used a T-bolt arrangement accessible from the rear of the parking brake and requiring the manipulation of a tool in a confined area. Such a procedure has not only proven to be awkward, but time-consuming as well.
It is a further requirement that the manual-release portion function without adding significantly to the maintenance schedule of the overall parking brake device. The T-bolt arrangement, previously discussed, experienced frequent maintenance problems because the manner in which it was used required compressing the springs which applied the parking brake, such springs having a spring force of significant proportions, thus resulting in excessive wear on the manual-release components.
Yet another requirement of the manually releasable parking brake is that its operation does not preclude separate operation of the tread brake unit. In many currently operating manual-release parking brake devices, such is the case, as for example, the T-bolt arrangement. Manual-release arrangements which work on the rod that connects to the brake lever and pulls the rod back to overcome the spring force in the opposite direction will, in turn, effect a release of the tread brake unit; such release being undesirable in many circumstances, for instance, while doing maintenance work only on the parking brake device.
As an even further requirement of the invention is that the manual-release portion be reset to the disengaged position automatically upon resumption of air pressure.